The present invention relates generally to wireless telecommunications networks, and more particularly to a broadband telecommunication system and network which employs atmospheric (i.e. free-space) laser transmission.
In the modern telecommunications market, there exists a vast array of products and services targeted for the needs and desires of consumers at every level. Many of these products and services necessitate a network infrastructure. For example, telephone service is mediated by the Public Switched Telephone Network (PSTN), also known as the Plain Old Telephone System (POTS).
Any-to-any connectivity is a fundamental organizing principle of the PSTN, i.e. any telephone subscriber should be able to call and communicate with any other telephone subscriber. The switching systems employed in the PSTN are almost completely digital. Fiber optic cables, copper cables, microwave links, and satellite links are used for data transmission. Transmission over the local loop is typically carried by copper-based T1 feeder or fiber optic cable. However the subscriber loop is still primarily implemented with copper UTP (unshielded twisted pair). Thus, the transmission bandwidth deliverable to a telephone subscriber is severely limited, typically less than 56,600 bits per second. At present, the PSTN bears the triple burden of conveying voice, fax, and data communications, and is nearly saturated in certain large metropolitan regions.
The Integrated Services Digital Network (ISDN) represents a step upward in speed relative to the PSTN. First time subscribers to ISDN service generally incur a cost for installation of an ISDN line which comprises upgraded copper wire. Computer users who access a corporate Intranet or the Internet through an ISDN line and ISDN modem experience increased performance relative to connecting through the PSTN.
A variety of communication applications such as interactive television, video telephony, video conferencing, video messaging, video on demand, high definition television (HDTV) and high-speed data services require broadband data transmission. In fact, many communication applications may require bandwidths high enough to exclude ISDN as a feasible medium for establishing a data connection.
Optical fiber offers significantly higher data transmission bandwidths than copper wire/media. However, fiber optic networks such as fiber to the curb (FTTC) and fiber to the home (FTTH) require new fiber optic cable to be run to every subscriber. Thus, the cost of implementing a fiber optic network may be exorbitant. Other alternatives for increasing the capacity of existing networks include Asymmetric Digital Subscriber Line (ADSL), Symmetric Digital Subscriber Line (SDSL), and Hybrid Fiber Coax (HFC), among others.
In general, all hard-wired networks are burdened with the requirement of laying cable to new subscribers/nodes. Furthermore, it is difficult to reconfigure the topology of an existing hard-wired network since cables are quite often buried underground, suspended from poles, or stung through the interstitial spaces of office buildings.
In contrast, wireless networks based on the radiation of electromagnetic energy through free space (i.e. the atmosphere) are able to service subscribers without incurring costs for laying cable to the subscribers. Many wireless telecommunication systems are organized as broadcast systems where a single transmitter sends an information signal to multiple receivers. For example, the Direct Broadcast Satellite (DBS) systems such as PrimeStar, Digital Satellite Service, etc. provide satellite broadcast of video channels to subscribers equipped with a receiving antenna (typically a dish antenna) and a set-top decoder. Wireless telecommunication systems and networks are widespread and numerous. Their numbers continues to increase in response to consumer demand. Thus, the radio spectrum is increasingly crowded resulting in degraded signal quality and/or increased subscriber costs.
In certain circumstances and for various reasons, a client/customer may desire point-to-point communication, i.e. the transmission of information between two points separated by a distance. For example, a microwave link between two central offices in the PSTN may be a point-to-point connection. Laser technology provides an admirable alternative to radio transmission for establishing broadband point-to-point communication due to the fact that lasers inherently generate narrowly focussed beams. Laser-based wireless systems have been developed for establishing point-to-point, bi-directional and high speed communication through the atmosphere. The range for such systems is typically 0.5 to 1.2 miles, with some systems achieving a range of 4 miles or more. The longest atmospheric communication path achieved with a point-to-point system exceeded 100 miles.
These point-to-point systems require a laser-based communication unit at each end of the point-to-point connection. A laser-based communication unit includes an optics package, a laser transmitter, an optical receiver, and a data interface package. The laser transmitter includes a laser for generating a laser beam, and modulating electronics for impressing a first information signal onto the laser beam. Quite often, the first information signal is a digital signal and ON/OFF keying is employed as the modulation scheme. The modulated laser beam is transmitted into the atmosphere by the optics package. Thus, the optics package is sometimes referred to as an optical antenna. The optics package also receives a second laser signal from the atmosphere, and provides the second laser signal to the optical receiver. The optical receiver includes photo-detection and demodulation electronics for recovering a second information signal from the second laser signal.
The data interface package is coupled to the laser transmitter, the optical receiver and to a communication bus. The data interface package is configured to send and receive data on the communication bus according to a pre-defined communication protocol. The data interface receives the first information signal from the communication bus and transmits the first information signal to the laser transmitter for modulation. The data interface also receives the second information signal from the optical receiver and transmits the second information signal onto the communication bus. Typically, a computer of some sort generates the first information signal and receives the second information signal. Thus, the computer generally requires a separate interface card/package in order to send/receive signals over the communication bus. For example, the communication bus may be the well-known Ethernet bus. In this case, the data interface in the laser-based communication unit is Ethernet compatible as is the interface card/package coupled to the computer.
In prior art laser-based point-to-point systems, the subsystems of the laser-based communication unit, i.e. the optics package, the laser transmiitter, the optical receiver, and the data interface package, are physically integrated into a common chassis. As will become apparent in the following discussion, the binding of all the sub-systems into a commnon chassis effects the design complexity of the communication unit and the installation procedures for the communication unit both of which impact the effective cost to the consumer.
In order to establish a point-to-point connection, two laser-based communication units must be configured so that their respective optical antennas achieve a line of sight (LOS) through the atmosphere. This generally requires that the units be installed at an elevated outdoor location such as a rooftop. Since, the communication unit includes active electronics, the user/client generally incurs a significant cost for providing a power connection to the installation site. This cost severely impacts the marketability of existing laser-based systems to home users and small business users.
The communication unit, being situated out of doors, may be exposed to a wide variation of temperature and weather conditions. Thus, the communication unit may require heating and/or cooling devices in order to protect the electronic subsystems. Furthermore, the chassis must generally be weatherproof. For example, the chassis should be designed to withstand rain, wind, and perhaps hail disturbances. Humidity from the ambient air may corrode internal metallic parts. These weather related constraints add to the overall cost of prior art laser-based communication units.
Laser-based communication units are massive and voluminous because of the colocation of transceiver electronics, data interface, and antenna optics in a common chassis. Care must be exercised to securely mount the chassis onto a supporting substrate. For example, the chassis often includes a base plate with holes which admit mounting screws. The cost of designing the chassis and its mounting structures contributes to overall cost of the communication unit.
After the communication unit has been mounted, an installer/user must adjust the angular orientation of the unit to achieve an optical line of sight (LOS) to a remote communication unit. The optical antenna of the local unit must be pointed at the optical antenna of the remote unit, and vice versa. This adjustment generally requires coordination between two installation personnel, one located at each site. In order to facilitate the LOS adjustment process, communication units typically include an external sighting scope. An installer/user looks through the sighting scope to determine the current direction of the optical antenna. The sighting scope is typically bore-sighted (i.e. calibrated) at the manufacturing facility. The installer/user adjusts the orientation of the communication unit until the remote antenna is centered in the cross-hairs of the sighting scope.
Since the bore-sighting (calibration) of the sighting scope may be comprised by physical disturbances to the sighting scope and/or communication unit, the laser beam transmitted by the optical antenna may not intercept the remote optical antenna when the unit is adjusted only on the basis of the sighting scope. The installer/user may have to execute a search procedure to achieve beam contact with the remote optical antenna. In other words, the installer/user may have to randomly adjust the orientation of the local unit while obtaining feedback from the person at the remote unit to determine when LOS has been achieved. The additional time required to conduct the random search in case of an insufficiently bore-sighted sighting scope significantly adds to the cost of installation.
Although a sighting scope may be bore sighted initially, e.g. in the factory or by trained personnel at a field site, the bore sighting (i.e. calibration) may be compromised over the passage of time. For example, thermal stresses and weathering (rain, hail, wind, etc.) may contribute to loss of bore sighting accuracy. Thus, the cost of bore sighting may be incurred more than once through the lifetime of the laser-based communication unit.
On occasion, the installer/user may desire to replace or upgrade one or more of the electronic subsystems of the communication unit. Since the electronic and optical sub-systems of the communication unit are combined in a common housing, the process of the accessing the electronic components/subsystems generally implies a physical disturbance of the optical antenna and the line of sight to the remote optical antenna. For example, replacement or upgrade of the data interface board may require the removal of an access panel. The pressures exerted in removing the access panel and exchanging boards may disturb the LOS of the communication unit. In some situations, the communication unit must be dismounted and transported to a repair facility for testing and repair. Thus, the investment in achieving LOS to the remote optical antenna may be lost when accessing electronics for maintenance, repair, and/or upgrade.
After accessing the electronics in the communication unit, the communication unit must generally be re-sighted at additional cost to the user/client. As with the initial sighting, the re-sighting generally requires two personnel: one situated at the local site to perform angular adjustments, and another situated at the remote site to confirm when LOS has been achieved. Thus, modification to the electronics of one communication unit generally requires two personnel to coordinate the LOS adjustment. This greatly increases the effective cost of repairing or modifying the electronics of the communication unit.
Laser-based systems are capable of maintaining a high-bandwidth point-to-point connection in some of the most severe inclement weather conditions. However, the cost of such systems is typically in the $10,000 to $20,000 dollar range, making them unsuitable for most home and business use.
Therefore, a need exists for a laser-based communication system which may be mounted more simply and efficiently than in prior art systems. Furthermore, a laser-based communication system which allows for accurate and efficient attainment of LOS to a remote unit is desired. Any method for circumventing the necessity of re-sighting the communication system upon repair or upgrade of electronics is greatly to be desired. Any method for simplifying user access to the electronic subsystems of the laser-based communication system is desirable. In general, a considerable need exists for a laser-based communication system which realizes significant cost reductions with respect to prior art systems.
Furthermore, in view of the problems associated with wired networks and radio-transmission based networks, a wireless laser-based telecommunication system is desired which provides a number of subscribers with high-bandwidth telecommunication services. In particular, a wireless laser-based telecommunication system is desired that enables a number of subscribers to communicate with a great number of subscribers. A wireless laser-based telecommunications system is further desired which reduces the cost to each subscriber, yet maintains high-speed, bi-directional, broadband, wide area telecommunications. A system is desired which does not require the huge installation costs of ISDN and fiber optics, and which does not require any of the electromagnetic broadcast bands in the radio spectrum. Such a network could be employed in a wide variety of applications such as telephony, data communications such as the Internet, teleconferencing, radio broadcast, and various television applications such as cable television, HDTV and interactive TV.
The present invention comprises a wireless optical transceiver system which includes a passive optical antenna coupled by optical fiber to an active electronics module. The transceiver system receives and transmits light beams from/to the atmosphere, and thereby communicates optically with a second optical transceiver. The fiber-optic isolation between an active electronics module and passive optical antenna has a host of implications which reduce the initial system cost and ongoing maintenance costs to the user. In particular, the passive optical antenna, free from the encumbering influence of active system components, may be installed more easily and efficiently. Line of sight to a target antenna may be achieved by disconnecting the optical fiber and visually observing through the optical path of the passive antenna. Furthermore, the isolation implies that a power connection is not longer required at the site of the optical antenna. This results in significant saving to the user/client.
In addition to an optical transceiver system, the present invention also contemplates receivers, transmitters, repeaters, switches, routers, etc. configured according to the principle of fiber-optic isolation between a passive optical antennas and active electronics modules. Such components are admirably suited for use in various network configurations such as broadcast networks, point-to-multipoint networks, etc due to their low cost, ease of installation and antenna sighting, modularity, and upgradability.